According to Wikipedia:
I was thinking about how cool would it be if there was a fictional but realistic account of life during the 1600s by a writer who lived during that period.
Depending on who you ask and whether you’re willing to extend the idea of “realism”: yes. Erich Auerbach wrote a whole took about the question: Mimesis. His main argument is (in a small nutshell) that it’s all a matter of looking at the representation of reality, rather than some spurious notion of what’s “realistic”. Dante, he points out, claimed that he was reproducing realistically the speech of his everyday, even if the Divine Comedy is not, of course, Flaubertian realism.
But if you insists on literary-historically defined era “realism,” probably the answer is no. Few authors saw the need to write stories about the “everyday”–whatever that is, really–given that everybody was living through the everyday every day. Perhaps the closest thing to realism was biography. If you look at James Boswell’s life of Johnson, for example, you’ll find plenty (oh, so much) mundane things that Boswell reports.
Daniel Defoe’s Journal Of The Plague Year might qualify? It’s not fiction but it’s pretty real.
Personal letters would probably be closer to the OP than any fiction of the time.
And diaries - Samuel Pepys is awesome.
Nice answer. Did not expect a whole book on the topic.
I very vaguely remember Lazarillo de Tormes being described as realist, in the same manner as Gil Blas, I guess. So, it seems most early realism might be considered to concentrate on criminality and those picturesque jolly brigands who made travel exciting rather than on the inner mental life of a launderess or a fabulous description of how pins are made by hand for 50 pages.
Well, there’s always the Tale of Genji, perhaps the world’s oldest novel, more or less realistic, and shockingly long for writing before people had computers. It was something of a freak anomaly, however, as we can find no evidence (despite a lot of written records) that anyone in Japan before wrote one. And afterwards, no such similar story came into being until Western Culture started showing an influence.
The Tale of Genji’s unrealistic elements are mostly confined to one person being absurdly awesome at everything. But given how the Imperial Court of the day was so self-absorbed, he’s pretty much a symbol of how much Japanese courtiers admired themselves. 
True. And Boswell’s diary is quite interesting, also.
What about Fielding’s Tom Jones?
Don Quixote is full of magical adventures. But it’s obvious their “magic” is in the mind of a man driven mad by reading too much fantasy…
What about Marco Polo’s Travels? It’s technically a travelogue but I’d argue it fits the definition of the OP - someone in the medieval world writing about and describing stuff that was going on at that time (with varying degrees of embellishment), and doing so in a long form narrative.
I agree with Journal of the Plague Year. Dafoe based it on the stories his uncle told about having lived through the year in question, not on his own diary or recollections.
StG
You might want to check death and birth dates on these guys, and then take another look at the OP.
How about Giacomo Casanova’s memoir? It’s a blend of fact and fiction. One historian said that, when he is talking about himself, it is pure fiction; when he is gossiping about other people, it is often surprisingly accurate.
Moll Flanders, by Daniel Defoe, 1772. First written account in English literature of women actually enjoying sex. *
Oh wait, that’s just a male fantasy. Never mind!
- , according to a college prof. I would have guessed it was in the Canterbury Tales, but evidently not.